<?php
//箭头函数
$pf = fn($i) => $i * $i;
echo $pf(6);

$su = fn($a, $b) => $a + $b;
echo '<br>', $su(10, 20);

//可变函数
function show() {
    echo 'hello show()';
}

echo '<br>';
$s = "show";
echo $s;
echo gettype($s); //string
echo gettype($s()); //NULL
